Interpretive Summary: Arundo donax, giant reed is an invasive weed in the Southwestern U.S. It is native to Mediterranean Europe. The Arundo wasp, Tetramesa romana, is from the native range in Europe and is a biological control agent of this invasive weed. Studies were conducted along the Rio Grande between Del Rio and Brownsville where the wasp has established and begun to spread. Based on our survey during a 14-month period from 2008 to 2009, numbers of the wasp peaked in early summer. The movement of the Arundo wasp indicates that it was likely to have first become established near Laredo and Eagle Pass, TX and dispersed up and down the river from these locations.

Technical Abstract:
The arundo wasp, Tetramesa romana, has been permitted as a biological control agent for the invasive perennial grass, Arundo donax. Evidence of adventive populations of the arundo wasp in the Lower Rio Grande Basin was confirmed with a spatio-temporal survey spanning more than 350 river miles. A total of 2,414 adult females of T. romana was collected over a 14-month 2008-2009 study period. This study documents the initial locations and regional expansion of two adventive populations of T. romana, centered around the cities of Eagle Pass and Laredo, TX. Peaks in T. romana density in August 2008 and June 2009 indicate a region-wide positive association between abundance of T. romana and high summer temperatures. Correlations between site specific abundance data and climate and suggest the presence of population-specific associations with both temperature and rainfall.